by Phil Peterson, NAMS-CMS

An engine oil analysis is a simple test to help determine the condition of a boat's engine. It is an inexpensive and convenient tool to help determine the condition of the engine without having a mechanic disassemble the engine. Test results can help determine if there are any coolant leaks, excessive wear in metal parts, and detect the presents of contaminants such as silicon, sodium and water. The viscosity of the oil is also tested to determine if it is within correct parameters.

A small amount of oil is drawn from the engine after the engine has been run up to temperature to insure that the oil and any contaminants are thoroughly mixed. The sample is then sent off to a lab for analysis and results are usually obtained in a few days.

Any readings outside of the below parameters may call for further investigation, or may be a reason to walk away from a potential boat purchase.

The best time to take an oil sample test is at an oil change, when the oil requires changing, which, of course, does not coincide with the time a boat is surveyed. However, the cost of the test may well be worth it 
Engine oil analysis is also helpful for boat owners to monitor their engine's long term condition. By taking a sample at the end of the season each year, a base line is established for an engine's condition, and any variances can quickly be detected. Having annual oil sample test results is also a good sales tool when it comes time to sell your boat.

Results from the lab are similar to the following:
Wear Metal Normal Range  Source
  Diesel Gas  
Iron 10 40 30 150 Cylinder walls/liners, valves shafts, gears
Copper 2 15 5 25 Bearings, bushings, may be high if application has a copper oil cooler
Lead 1 8 2 12  Bearing, leaded gasoline
Aluminum 1 8 2 12  Pistons
Chromium 1 4 2 8 Piston rings
Silicon 1 14 1 14 Airborne dirt, may be high due to silicon containing additives
Sodium 1 25 1 50  Some oils contain sodium, but it is also added to antifreeze as a corrosion inhibitor
Water Negative Negative Condensation, coolant leak, (antifreeze may be detected and not water, due to the water being lost as vapor

Phil Peterson is a Certified Member of the National Association of Marine Surveyors, and lives in Bayfield, Wisconsin. He can be reached at 715-779-0254.